U.S. patent application number 10/663103 was filed with the patent office on 2005-03-17 for system, method, and apparatus for establishing headroom for a mobile station.
Invention is credited to Bi, Hao, Reed, John D..
Application Number | 20050059421 10/663103 |
Document ID | / |
Family ID | 34274276 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050059421 |
Kind Code |
A1 |
Reed, John D. ; et
al. |
March 17, 2005 |
System, method, and apparatus for establishing headroom for a
mobile station
Abstract
A system, method, and apparatus for establishing headroom for a
mobile station operating in a wireless communication system by
determining (230) a communication channel variance condition and
establishing (245) a headroom value based on the communication
channel variance condition. The headroom value may be further
revised by determining (260) if a battery condition in a mobile
station relates to a low battery level and increasing (265) the
headroom value in order to decrease the maximum data rate.
Modifications to headroom allow data rates to be tailored to
specific channel variance conditions and battery conditions.
Inventors: |
Reed, John D.; (Arlington,
TX) ; Bi, Hao; (Wheeling, IL) |
Correspondence
Address: |
MOTOROLA INC
600 NORTH US HIGHWAY 45
ROOM AS437
LIBERTYVILLE
IL
60048-5343
US
|
Family ID: |
34274276 |
Appl. No.: |
10/663103 |
Filed: |
September 16, 2003 |
Current U.S.
Class: |
455/522 ;
455/69 |
Current CPC
Class: |
H04W 52/367 20130101;
H04W 52/267 20130101; H04W 52/30 20130101; H04L 1/0002 20130101;
H04W 52/241 20130101; H04W 52/248 20130101 |
Class at
Publication: |
455/522 ;
455/069 |
International
Class: |
H04B 007/00 |
Claims
We claim:
1. A method for establishing headroom for a mobile station
operating in a wireless communication system comprising the steps
of: determining a communication channel variance condition; and
establishing a headroom value based on the communication channel
variance condition.
2. A method according to claim 1 wherein a mobile station performs
the steps of determining and establishing.
3. A method according to claim 2 wherein the mobile station
determines a maximum data rate based on the headroom value and
sends the maximum data rate to a base station.
4. A method according to claim 2 wherein the mobile station
determines a maximum data rate based on the headroom value and
sends a rate adjustment request to a base station.
5. A method according to claim 2 further comprising the steps of:
detecting a battery condition of the mobile station; and modifying
the headroom value based on the battery condition.
6. A method according to claim 5 wherein the step of modifying the
headroom value based on the battery condition comprises:
determining if the battery condition relates to a low battery
level; and if the battery condition relates to a low battery level,
increasing the headroom value.
7. A method according to claim 2 wherein the step of determining a
communication channel variance condition includes measuring a
variance in a primary pilot power.
8. A method according to claim 1 wherein a base station performs
the steps of determining and establishing.
9. A method according to claim 8 wherein the step of determining a
communication channel variance condition includes examination of an
inner loop power control bit stream.
10. A method according to claim 8 further comprising the step of:
sending the headroom value to the mobile station.
11. A method according to claim 8 further comprising the step of:
determining a data rate assignment for a mobile station using the
headroom value and sending the data rate assignment to the mobile
station.
12. A mobile station comprising: means for determining a
communication channel variance condition; and means for
establishing a headroom value based on the communication channel
variance condition.
13. A mobile station according to claim 12 further comprising:
means for determining a maximum data rate based on the headroom
value; and means for sending the maximum data rate to a base
station.
14. A mobile station according to claim 12 further comprising:
means for determining a maximum data rate based on the headroom
value; and means for sending a rate adjustment request to a base
station.
15. A mobile station according to claim 12 further comprising:
means for detecting a battery condition of the mobile station; and
means for modifying the headroom value based on the battery
condition.
16. A wireless communication system comprising: a base station; at
least one mobile station; means for determining a communication
channel variance condition; and means for establishing a headroom
value based on the communication channel variance condition.
17. A wireless communication system according to claim 16 further
comprising: means for determining a data rate based on the headroom
value.
18. A wireless communication system according to claim 17 further
comprising: means for sending the data rate between the base
station and said at least one mobile station.
19. A wireless communication system according to claim 16 further
comprising: means for determining a battery condition of said at
least one mobile station; and means for modifying the headroom
value based on the battery condition.
20. A wireless communication system according to claim 19 further
comprising: means for determining a data rate based on the headroom
value; and means for sending the data rate between said at least
one mobile station and the base station.
Description
FIELD OF THE DISCLOSURE
[0001] This disclosure relates generally to wireless communications
technology, and more particularly to power control of wireless
transmissions under varying channel conditions.
BACKGROUND OF THE DISCLOSURE
[0002] Electronic communications, especially wireless
communications, occur under varying channel conditions. In order to
maintain a voice or data connection under unknown and changing
channel conditions, many wireless communication system transmitters
apply a margin. This margin reserves room for fading and other
common adverse channel conditions during communication by ensuring
that the quality of communications is not degraded below an
accepted level if the channel is adversely affected by certain
temporary severe channel attenuations. Thus, margin provides some
insurance under adverse channel conditions.
[0003] A higher margin results in a higher level of robustness
during changing channel conditions, but at the cost of a lower
achievable data rate. Conversely, a lower margin results in a
higher achievable data rate, but at the cost of increased
vulnerability under changing channel conditions.
[0004] In many wireless communication system environments, headroom
is used to provide margin. Headroom is the difference between the
maximum power of the transmitter and the transmission power level
required for a particular data rate. When a mobile station would
like to establish a communication channel and has data in its
buffer, the mobile station determines its maximum transmission
power, subtracts the headroom, and uses the remaining available
transmit power to determine a maximum data rate. Thus, the maximum
data rate has margin built in to provide some protection against
varying channel conditions. To date, headroom has been a constant
value established to account for many (but not all) common adverse
variances in channel conditions. One common model of adversely
varying channel conditions is the Rayleigh fading model.
[0005] Although there are occasions where the channel varies more
than the Rayleigh fading model predicts, there are many times when
channel conditions do not vary as severely as Rayleigh fading.
Under more benign channel conditions, such as Rician fading channel
conditions, the standard headroom may be excessive. In other words,
a transmission through more benign channel conditions would not
exceed the maximum bit error rate even if the headroom were
lower.
[0006] Excessive headroom leads to, among other things, lower
achievable data rates and a correspondingly lower battery drain. On
the other hand, inadequate headroom leads to a lower level of
robustness under changing channel conditions. Thus, there is a
desire for transmission power control that reduces instances of
excessive headroom to achieve higher data rates while maintaining
an acceptable bit error rate over varying channel conditions. The
various aspects, features and advantages of the disclosure will
become more fully apparent to those having ordinary skill in the
art upon careful consideration of the following Drawings and
accompanying Detailed Description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows a simplified wireless communication system and
sample packet communication transmissions according to a first
preferred embodiment.
[0008] FIG. 2 shows a flow chart used by a mobile station to adjust
headroom according to the first preferred embodiment.
[0009] FIG. 3 shows a flow chart used by a base station to assign
headroom according to the first preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] A system, method, and apparatus for establishing headroom
for a mobile station operating in a wireless communication system
by determining a communication channel variance condition and
establishing a headroom value based on the communication channel
variance condition. The headroom value may be further revised by
determining if a battery condition in a mobile station relates to a
low battery level and increasing the headroom value in order to
decrease the maximum data rate. Modifications to headroom allow
data rates to be tailored to specific channel variance conditions
and battery conditions.
[0011] FIG. 1 shows a simplified wireless communication system 100
and packet communication transmissions according to a first
preferred embodiment. This first preferred embodiment depicts a
set-up and transmission for a data stream between a mobile station
110 and a base station 190 operating in a CDMA2000 wireless
communication system. Other wireless communication systems use
similar data transmission set up protocols, and the principles
described in this specification could be applied to other wireless
communication systems. When the mobile station 110 has data in its
buffer to send, the mobile station 110 sends a data transmission
request 130 to its serving base station 190. In this first
preferred embodiment, the contents of the data transmission request
include the mobile station's available transmit power. Preferably,
the data transmission request also includes the amount of data in
its buffer. Alternate embodiments may include the maximum data rate
that the mobile station would like to transmit on the reverse link,
and may include related parameters such as the amount of data in
its buffer, the rate of its increase, and the headroom value.
[0012] After receiving and decoding the data transmission request
130, the base station 190 transmits a request grant 140 to the
mobile station 110 that includes: a channel assignment, a data rate
assignment for the mobile station or other parameters rated to data
rate, and may optionally include a headroom assignment for the
mobile station.
[0013] Next, the mobile station 110 sends a data transmission 150
to the base station 190 on the assigned channel at the specified
data rate. During data transmission 150, the mobile station may
detect changes in circumstances that cause it to request a change
from the current transmission data rate. If so, the mobile station
transmits a rate adjustment request 160. In the first preferred
embodiment, the rate adjustment request takes the form of a mobile
status indicator bit (MSIB) used in a rate control mode of
CDMA2000.
[0014] FIG. 2 shows a flow chart 200 used by a mobile station to
adjust headroom according to the first preferred embodiment. The
mobile station 110 shown in FIG. 1 can implement this flow chart
200. In step 210 the mobile station receives data in its buffer to
send. At this point, the headroom value (P.sub.h) is set to a
default value in step 220. In the first preferred embodiment, the
default value is the last headroom assignment received from the
serving base station. If the serving base station does not provide
headroom assignments, the mobile station default would be a
predetermined value, such as 5 dB, specified by the network that
accounts for most common fading channel conditions.
[0015] At step 230, the mobile station detects its communication
channel variance conditions. Measurements of primary pilot power
variance using a moving window can be used to estimate where the
varying channel conditions reside along the spectrum of severe
(worse than Rayleigh fading channels) to benign (high K-factor
Rician fading channels). Alternate and additional channel
measurements include: primary pilot power variance using a variable
window size, estimation of the fading period and fade depth, a
peak-to-average estimate within an adaptive measurement interval,
and other measurements that relate to channel variance.
[0016] Step 240 determines whether the actual channel conditions
are benign. If channel conditions are benign, the headroom P.sub.h
is modified in step 245 based on the detected communication channel
variance conditions. Additionally, the duration of the scheduling
interval can affect the headroom. For example, scheduling over
longer transmission times, which has a higher risk of channel
variance, requires higher headroom. Headroom modifications can be
implemented using an equation, a look-up chart or matrix, or other
known ways to map at least one input to an output. In this first
preferred embodiment, the headroom P.sub.h is originally set to the
latest headroom assignment from the base station in step 220, and
any modifications due to benign channel conditions decrease the
value of the headroom P.sub.h' It is possible, though, to
initialize the headroom value at the highest allowed value such as
5 dB and decrease the headroom based on detected channel
conditions. Alternately, the headroom value could be initially set
to a middle value with the modifications moving the headroom either
up or down depending on detected channel conditions.
[0017] Once the headroom is modified, or if the headroom is not
modified because channel conditions are not benign, step 250
detects a battery condition of the mobile station. Greater headroom
values result in reduced maximum data rates compared to lower
headroom values. If, however, the battery is low as determined in
step 260, it may be advantageous to increase the headroom P.sub.h
in order to force a lower data rate. Because the increased headroom
does not affect the range of power control, the quality of the
transmitted signal will be adequate, while the mobile station
maintains a lower average power and thus produces a power savings.
The savings can be used, for example, to extend the duration of a
mobile station voice call. Thus, step 265 modifies the headroom
value based on the detected battery condition.
[0018] After the headroom value has been modified, or if the
headroom value is not modified because the battery is not low, step
270 sends a request with the appropriate values. In the first
preferred embodiment CDMA2000 system, the request takes the form of
either a data transmission request or a rate adjustment request as
previously described with reference to FIG. 1. In a data
transmission request, the mobile station includes the available
transmit power and the amount of the data in its buffer. Some
releases of CDMA2000 expect the data transmission request to
include the mobile station's maximum data rate rather than its
available transmission power and amount of data in its buffer. In
that case, the mobile station would subtract the headroom value
from its maximum transmit power to result in an available transmit
power value. This available transmit power value maps to a maximum
data rate which would be included in the data transmission request.
Another alternative would be to transmit the maximum transmit
power, the headroom, the amount of the data in the buffer, and its
rate of increase.
[0019] If the request is a rate adjustment request as supported by
some modes of operation, such as the CDMA2000 rate control mode,
the mobile station calculates a desired transmission rate based on
the modified headroom value and other parameters mentioned above,
and compares this desired rate to its current transmission rate. If
the desired rate is different than the current rate, the mobile
station will inform the base station by, for example, transmitting
an indicator bit (MSIB) as its rate adjustment request.
[0020] Regardless of the information in the request, the mobile
station is capable of modifying its headroom under various
predetermined conditions, such as benign channel conditions or low
battery conditions. Reduction in headroom under benign channel
conditions allows higher peak data rates, which promotes improved
performance. On the other hand, increasing headroom during lower
battery conditions provides lower peak data rates, which extends
battery life.
[0021] If the mobile station desires to send two or more data
streams (or hold voice and data connections at the same time), an
addition degree of freedom allows the mobile station to
deliberately increase the headroom on one of the data streams to
de-prioritize that data stream. This would result in, for example,
a longer time to transmit a text message from the mobile station
but allow a digital picture to be transmitted at an optimum data
rate.
[0022] The mobile station, or the base station, or both the mobile
station and base station can adjust the headroom. FIG. 3 shows a
flow chart 300 used by a base station to adjust headroom according
to a first preferred embodiment. The base station 190 shown in FIG.
1 can implement this flow chart 300. In step 310, the base station
receives a data transmission request from a mobile station, which
includes the mobile station's available transmit power and
preferably the amount of data in the mobile station's buffer.
Optionally, the request can include the amount of data in the
mobile station's buffer plus its maximum transmit power and
headroom, which can be used to calculate the mobile station's
available transmit power. The rate of increase of the amount of
data in the mobile station's buffer is also helpful.
[0023] In step 320, the base station estimates the communication
channel variance conditions. Examination of an inner loop power
control bit stream can be used to determine where the varying
channel conditions reside along the spectrum including severe
(worse than Rayleigh fading channels) and benign (high K-factor
Rician fading channels). Other measurements that may affect the
determination of channel conditions are measurements from a pilot
channel of the mobile station.
[0024] Step 330 establishes the headroom of the mobile station
based on the estimated communication channel variance conditions.
If the channel conditions are benign, the headroom P.sub.h is less
than if the channel conditions were severe. Additionally, the
duration of the scheduling interval can affect the headroom. For
example, longer scheduling intervals produce longer transmission
times, which means a higher risk of channel variance, which leads
to higher headroom. Headroom can be established using an equation,
a look-up chart or matrix, or other known ways to map at least one
input to an output. Once the headroom is established, the headroom
is sent to the mobile station in step 340. In certain
implementations, sending the headroom to the mobile station
independently is unsupported or undesirable. Thus, step 340 is
optional.
[0025] Going to step 350, after the base station receives the data
transmission request in step 310, the base station obtains the
mobile station's available transmit power either directly or
indirectly from information in the request packet. In step 360, the
base station determines the data rate for the mobile station based
on the headroom (established in step 330) and the mobile station's
available transmit power. In step 370, the base station reserves
reverse link capacity, and the base station sends a request grant
that includes the mobile station data rate assignment in step 380.
The request grant can also include the established headroom
value.
[0026] According to the first preferred embodiment, both the base
station and the mobile station participate in headroom adjustments.
The base station's request grant 140 (in FIG. 1) assigns the mobile
station 110 a data rate based on the headroom determined by the
base station 190. The mobile station's headroom determination is
used in a rate control mode where the mobile station 190 calculates
a desired transmission rate based on the adjustable headroom value
and other parameters, and compares this desired rate to its current
rate. If the desired rate is larger than the current rate, for
example, the mobile station will inform the base station by
transmitting an indicator bit (MSIB) in its rate adjustment request
160.
[0027] In a second alternative embodiment the mobile station and
base station use a slightly different methodology to participate in
headroom adjustments. Before the data transmission request 130 (in
FIG. 1), the base station 190 has already assigned a headroom value
to the mobile station. Thus, setting the headroom value to a
default in step 220 (in FIG. 2) is merely setting the headroom
value to the latest headroom value assigned by the base station.
The base station further updates and refines the headroom value in
step 330 (in FIG. 3) and sends that headroom assignment to the
mobile station. This loop between the mobile station and the base
station can occur outside of the data transmission set up protocol,
and the headroom adjustment loop can be applied to other signaling
protocols in a wireless communication system.
[0028] A third alternate embodiment allows the mobile station to
adjust its headroom without the base station's participation. The
flow chart 200 (in FIG. 2) enables a mobile station to
independently adjust its headroom by setting its headroom value to
a standard default value such as 5 dB rather than a value assigned
by the base station. Preferably, the standard default value is
specified by the network and stored in the mobile station through a
layer 3 message during call setup.
[0029] In a fourth alternate embodiment, a base station can adjust
headroom independently if the mobile station is equipped to accept
headroom assignments (not all mobile stations are so equipped).
[0030] Thus, the method and apparatus for headroom adjustment
provides a margin and related data rate tailored to varying channel
conditions, the particular data streams from the mobile station,
and the mobile station battery level. This margin more efficiently
controls power to promote faster data rates when channel conditions
are favorable and increase battery life when the battery level is
low.
[0031] While this disclosure includes what are considered presently
to be the preferred embodiments and best modes of the invention
described in a manner that establishes possession thereof by the
inventors and that enables those of ordinary skill in the art to
make and use the invention, it will be understood and appreciated
that there are many equivalents to the preferred embodiments
disclosed herein and that modifications and variations may be made
without departing from the scope and spirit of the invention, which
are to be limited not by the preferred embodiments but by the
appended claims, including any amendments made during the pendency
of this application and all equivalents of those claims as
issued.
[0032] It is further understood that the use of relational terms
such as first and second, top and bottom, and the like, if any, are
used solely to distinguish one from another entity, item, or action
without necessarily requiring or implying any actual such
relationship or order between such entities, items or actions. Much
of the inventive functionality and many of the inventive principles
are best implemented with or in software programs or instructions.
It is expected that one of ordinary skill, notwithstanding possibly
significant effort and many design choices motivated by, for
example, available time, current technology, and economic
considerations, when guided by the concepts and principles
disclosed herein will be readily capable of generating such
software instructions and programs with minimal experimentation.
Therefore, further discussion of such software, if any, will be
limited in the interest of brevity and minimization of any risk of
obscuring the principles and concepts according to the present
invention.
* * * * *